The experiments will make use of the specificity of antitubulin drugs, such as colchicine and vinblastine, to study the organization of tubulin in dividing and nondividing cells and in normal and transformed cells. The existence of nonmicrotubular aggregates of tubulin in a transformed rat cell line (442 cells) and in surf clam eggs will be investigated by studying the action of various antitubulins. This will be done by isolating these structures by centrifugation and then determining the content of tubulin by a gel electrophoresis technique. In order to interpret the response of tubulin in different cells to various antitubulins, a systematic study of the effects of these drugs in vitro will be done. This study will use analytical ultracentrifugation to determine the effects of different drugs on the states of aggregation of tubulin. Dose-response curves will be determined by quantitative procedures in vitro and in vivo. The in vitro analysis will use turbidity measurements and electron microscopy to measure microtubule and aggregate concentrations. Differences in the response to drugs will be used as the basis for further investigations into the state of tubulin cells. We will examine the extent of tyrosylation and phosphorylation of tubulin aggregates obtained before and after drug treatment. From these experiments we hope to explain the basis of action of anticancer drugs which are thought to effect microtubules.